China’s high-tech building industry may have been flexing its ample construction muscles for the past decade in places like Beijing and Shanghai, but a few hundred miles away in Shanxi province, an estimated three million people still live in caves.
These simple homes often dot the countryside in small, hard-to-find clusters, but in places like Lijiashan, where hundreds of caves scale nine different levels of a hillside, it is possible to find whole communities made up entirely of cave dwellers.
People have been living in caves in Shanxi for around 5,000 years, and it is believed that at one stage a quarter of the population lived underground. These days around one-twelfth of Shanxi-ers live in caves - still a remarkable number - and for many of them, life is almost as it was for their ancestors.
Lijiashan, a 550-year-old cave village, hugging a hillside set back from the Yellow River, is typical. Like most cave communities, it was hooked up to the national grid some time ago, but there is still no running water or sewage system, meaning locals are as reliant as ever on the raging muddy waters of the nearby Yellow River. The village's nine terraced levels are linked by stone stairways that date back to the Ming Dynasty, and most homes still have paper windows rather than glass panes. Inside, their owners sleep on large stone beds, known as kang; cool in the summer, but with cavities underneath so that fires can be lit inside them during the winter months.
It all sounds like something from a history book, but there are qualities here that would impress the most forward-thinking of modern architects. Intrinsically linked to the earth, cave homes are, unsurprisingly, pretty kind to the environment. Surrounded by thick earthen layers, cave houses are very well insulated, ensuring residents are protected against freezing winters and scorching summers (not to mention noisy neighbours) without racking up huge electricity bills. Less building materials also makes cave homes very cheap to make and, importantly for this part of the world, they also afford better protection from natural disasters such as earthquakes.
Current cave-dwelling numbers may sound high, but in fact these communities are far from thriving. Lijiashan once housed 600 families. Now there are just over 40. Most caves lie abandoned or are used to house the livestock of local farmers, and Lijiashan's school, with caves for classrooms, currently has just four pupils.
Lack of home comforts is one obvious reason for kids here to jump ship at the earliest opportunity. Remoteness is another - Lijiashan is an eight-hour, triple-bus journey from Taiyuan, Shanxi's capital city - but the main reason the youngsters have scarpered is that living in caves just is not very cool.
Mr Li's family has lived in Lijiashan for six generations. After his kids left the village to find work elsewhere, he and his wife converted their 180-year-old courtyard home into a guesthouse with cave bedrooms where Chinese art students stay when they come to paint the unusual village landscape.
"The only people left here now are old people," he said. "As soon as the children grow up they leave. They don't mind living here by the Yellow River. Sometimes they just move down the road. But they want to live in new apartments, not in these old caves."
You can get to Lijiashan from either Taiyuan or Pingyao, via the mining town of Lishi and the ancient trading port of Qikou. Occasionally there are direct buses from Taiyuan to Qikou, but do not bank on it. Taiyuan is about an eight-hour train journey from Beijing.
The article 'The cave dwellers of 21st-century China' was published in partnership with Lonely Planet.